The present invention relates to a diaphragm type pressure sensor using a piezoresistivity effect, and more particularly to a pressure sensor having a diaphragm on which diffused resistors are formed as a sensing element that measures pressure exerted on the diaphragm, using the piezoresistivity effect. The present invention relates even more particularly to such a diaphragm type pressure sensor provided with a detector for sensing diaphragm breakage.
A known semiconductor pressure sensor includes a silicon diaphragm whose one surface is provided with a diffused resistor thereon which varies in resistance due to stress from pressure applied thereto, thereby converting the applied pressure to a corresponding electric signal. This sensor is relatively small and has excellent sensitivity. Integrated circuit manufacturing techniques allow many such uniform characteristic sensors to be easily produced. These excellent sensor features have been brought to many persons' attention so that research on this sensor towards practical use has been carried out in many factories and research institutes. For example, in the field of automobile manufacturing, applications are being made toward the measurement of intake air pressure of an engine for superior accuracy and response.
However, one problem with this sensor is that its diaphragm, made of a semiconductor material such as silicon, is liable to be broken due to its fragility by a sudden negative change in pressure exerted on the diaphragm which sudden change is caused for example by a driver suddenly stepping on the accelerator pedal when the sensor is used for measuring the pressure of intake air into an engine, or by a sudden change in exhaust gas pressure caused by an afterburner when the sensor is used with an exhaust gas recirculation system. Further, the diaphragm tends to deteriorate due to aging thereof. Thus, when using such a sensor with an engine control system, it is necessary to detect diaphragm breakage at as early a stage of breakage as possible in order to cope with the same and ensure safe automobile driving.